This is a multicenter collaborative study to determine the sensitivity, specificity, positive predictive value, and negative predictive value of contrast enhanced spiral computed tomography (spiral CT) for the diagnosis of acute pulmonary embolism (PE). PE is common, yet frequently undiagnosed and fatal. Ventilation/perfusion lung scans are the most commonly used test. However, they are nondiagnostic in 72 percent of patients with suspected PE, and in 57 percent of patients with proven PE. Pulmonary angiography is the currently definitive diagnostic test, but there is hesitancy to use it because of morbidity, discomfort, cost, and lack of availability in community hospitals. Contrast enhanced spiral CT is a nearly noninvasive test that offers the possibility of a definitive diagnosis of PE by showing the outline of the embolus in a pulmonary artery. However, its utility in the diagnosis of PE is unknown. Even though spiral CT has not been adequately validated, physicians at many hospitals now use it as a definitive and only diagnostic test for PE, or as a definitive test in patients in whom the ventilation/perfusion lung scan is nondiagnostic. This could lead to overtreatment or undertreatment, both of which have serious potential complications. The role of spiral CT in the diagnosis of PE requires an accurate evaluation which will be made in this investigation through the use of pulmonary angiography, the ventilation/perfusion scan, and compression ultrasound of the legs. Venous ultrasonography has been incorporated into this protocol because it permits a strategy of management based on venous thromboembolic disease (PE or deep venous thrombosis) in some patients. The strengths of this proposal are: 1) the importance of the problem of PE in terms of lives lost from underdiagnosis, and major bleeding from overdiagnosis 2) the potential applicability of a new technology for the diagnosis of PE that will have widespread availability 3) The protocol parallels standard diagnostic strategy, without subjecting the patients to risk entirely for the acquisition of data and 4) the team of investigators is strong and experienced.